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Phytochrome a Mediates Blue Light and UV-A-Dependent Chloroplast Gene Transcription in Green Leaves

Louis Chun, Alana Kawakami and David A. Christopher
Plant Physiology
Vol. 125, No. 4 (Apr., 2001), pp. 1957-1966
Stable URL: http://www.jstor.org/stable/4279826
Page Count: 10
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Phytochrome a Mediates Blue Light and UV-A-Dependent Chloroplast Gene Transcription in Green Leaves
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Abstract

We characterized the photobiology of light-activated chloroplast transcription and transcript abundance in mature primary leaves by using the following two systems: transplastomic promoter-reporter gene fusions in tobacco (Nicotiana tabacum), and phytochrome (phyA, phyB, and hy2) and cryptochrome (cry1) mutants of Arabidopsis. In both dicots, blue light and UV-A radiation were the major signals that activated total chloroplast and psbA, rbcL, and 16S rrn transcription. In contrast, transcription activities in plants exposed to red and far-red light were 30% to 85% less than in blue light/UV-A, depending on the gene and plant species. Total chloroplast, psbA, and 16S rrn transcription were 60% to 80% less in the Arabidopsis phyA mutant exposed to blue light/UV-A relative to wild type, thus definitively linking phyA signaling to these photoresponses. To our knowledge, the major role of phyA in mediating the blue light/UV-A photoresponses is a new function for phyA in chloroplast biogenesis at this stage of leaf development. Although rbcL expression in plants exposed to UV-A was 50% less in the phyA mutant relative to wild type, blue light-induced rbcL expression was not significantly affected in the phyA, phyB, and cry1 mutants. However, rbcL expression in blue light was 60% less in the phytochrome chromophore mutant, hy2, relative to wild type, indicating that another phytochrome species (phyC, D, or E) was involved in blue light-induced rbcL transcription. Therefore, at least two different phytochromes, as well as phytochrome-independent photosensory pathways, mediated blue light/UV-A-induced transcription of chloroplast genes in mature leaves.

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